The operating regularity of the stepper motor of thermal inkjet printers and its application in the China national accreditation service 2017ZO146 altered documents identification proficiency test.

With the continuous innovation of inkjet printing technology, the methods of using inkjet printers for falsification have also constantly evolved, leading to increasing difficulties in identifying printing alterations made by the same inkjet printer. This paper mainly studies the operating regularity of the stepper motor of inkjet printers to determine the operating mechanism of inkjet printers and thus to identify whether documents had been tampered with. To detect the operating track of the stepper motor, 154 documents printed by 22 different brands and models of thermal inkjet printers were studied according to the periodic morphological characteristics of ink marks and the track of the stepper motor during different printing processes. As a result: ① the maximum gauge of 22 printheads was found to be different and ② the different distribution of ink marks were mainly affected by the direction and speed of the stepper motor. The track of the stepper motor was able to be determined by the periodic morphological characteristics of the ink marks combined with the maximum gauges, and could be used to judge how many times a document was printed. The observed regularities were evaluated by the CNAS 2017ZO146 test, a national proficiency test in China. In conclusion, using the summarized operating regularities of the stepper motor, it is possible to identify printing alterations made by the same thermal inkjet printer.